Separation of meta-xylene from isomeric xylene mixtures



June '28, 1960 SEPARATION NOILV'I'IILSIG NCE METATXYLENE PRODUCT NOLLV'TILLSIG FEED produced.

SEPARATION OF META-XYLENE FROM ISOlVIERIC XYLENE MIXTURES John A. Spence, San Anselmo, Calif., assigner to California Research Corporation, San Francisco, Calif., a corporation of Delaware Filed Oct. 30, 1956, Ser. No. 619,290

`6 Claims. (Cl. 260-674) The present invention relates to the production of highpurity meta-xylene from hydrocarbon mixtures comprising meta-xylene and at least one other xylene isomer, and particularly to an improved method for selectively sulfonating the meta-xylene present in such mixtures, and for separating meta-xylene from the resulting xylene sulfonic acids. Y

Selective sulfonation has been-used in various prior art processes for producing meta-xylene from mixtures comprising other xylene isomers. These processes are based on the fact that meta-xylene is more readily sulfonated than the other xylenes, and on the fact that xylene sulfonic acids resulting from sulfonation can be selectively hydrolyzed to the corresponding xylenes.

, Thus, it has been known heretofore, that the partial sulfonation of a crude xylene fraction, for example, with `a moderately strong sulfuric acid under conditions preventing complete sulfonation could be made to dissolve or sulfonate a substantial portion of the meta-xylene content of the crude xylene, without the accompanying sulvfon-ation of nearly as substantial a portion of the other xylenes. It has also been known that the sulfonic acid resulting from this sulfonation could be separated from the unsulfonated oil, that the separated unsulfonated oil could be sulfonated to produce an additional sulfonic acid fraction, and that the xylenes present in the two different sulfonic acid fractions -thus obtained could be separated by selective hydrolysis, fractional crystallization, or a combination of the two procedures.

It is apparent that the selectivity of sulfonation of the meta-xylene present in the original mixture is an important factor in determining the purity of the recovered meta-xylene. Increasing the percentage of meta-xylene s ulfonic acid present in the xylene sulfonic acids resulting from sulfonation increases the amounts of meta-xylene that can be separated from the xylene sulfonic acids, and reduces the -amounts of undesired xylene isomers that will separate out with the metaxylene during the separation step. Heretofore, the degree of meta-xylene sulfonation selectivity in these sulfonation processes has left muchA to -be desired, and the resulting undue amo-unt of sulfonation of undesired xylene isomers has meant inecient and costly utilization of acid, and other process ineiiiciencies. In the f-ace of the large and growing commercial demand for high-purity meta-xylene, i.e., meta-xylene f at `least 95% purity, eicient production thereof is of great importance. This is particularly so in large scale operations requiring high-purity meta-xylene for the production of intermediates for products that must enter price competition with similar-products, for example, processes using high-purity meta-xylene for the production of isophthalic acid for subsequent conversion to plastics.` Accordingly, -it is an object of the present invention tov provide an improvide process comprising selective sulfonation in which the meta-xylene sulfonation selectivity inthe sulfonation step and the efliciency of yacid utilization are high, and with which meta-xylene of at least 95% purity may be nited States Patent to enrich the acid phase with dissolvedmeta-xylene l In Iaccordance with the present invention there is provided a process for producing meta-xylene of high purity from a first mixture comprising meta-xylene and at leastl one other xylene isomer which comprises: contacting said rst. mixture ina rst contacting zone with a recycle streamcomprising xylene sulfonic acid and dilute sulfuric acid; passing the resulting second mixture to a second conphase; and recovering meta-xylene from the remaining portion of said separated second phase.

The novel features of the present invention are set yforth with particularity in the appended claims. The invention will best be understood, however, both as to organization and operation, and additionalobjects and advantages thereof will be apparent, from the lfollowing description, when read in connection with the accompanying drawing. The single figure there shown is a diagrammatic view, including ow paths, of an embodiment of the present invention.

The feed stocks for the process of the present invention may comprise lfrom about 20% by volume to about 80% by lvolume of meta-xylene. attractive for producing high-purity meta-xylene lfrom `feed stocks vhaving Ia meta-xylene concentration of from aboutA 35% l,by volume to about 70% by volume,A The feed stocks for the process may be derived, for example, lfrom Vhydroformed non-aromatic petroleum fractions. These Viced stocks may be reduced in undesiredxylene isomer'pontent prior to being used in the presentprocess by conventional methods capable of removing the undesiredisomers. For example, the `orthp-xylene content may beu reduced by distillation, although meta-xylene and para-,xylene cannot be separated economically by presently available distillation methods. The composition of typical lfeed stocks suitable for use inthe practice of the present invention is indicated in the following examples:

Referring now to the drawing, thehydrocarbon feed mixture containing meta-xylene and-fat least one other xylene isomer Vis passed through line 1 to rst contacting or mixing zone 2, where it is contacted with a recycle stream passed through line 3 from reactor-settler 9. This recycle stream corrtainsV xylene sulfonic acids, free kacid and a minor amount of dissolved, unsulfonated oil but is substantially free vof unsulfonated oil as a separate phase. recycle stream are mixed vigorously to facilitate the transfer of meta-xylene to .the recycle acid phase, thereby enriching Vthe recycle acid phase -with meta-xylene. The operating conditions .of the process are adjusted tomain.

tain the acid concentration and temperature of tht-.recycle f stream at values, `for example, 81% H2804 Vand ',1509F.

tive as a sulfonating agent, Vthereby making it possible The process is particularlyV In first mixingzone 2 thefeed stream and the to sulfonation, which is accomplished with fresh concentrated acid in a subsequent step.

The etiluent from first mixing zone 2 is passed through line 4 and heat-exchanger 5 to second contacting or mixing zone 6. Heat-exchanger 5 is provided to cool the stream flowing in line 4 by removing heat therefrom to control the temperatures in reactor-settler 9 and hence in the recycle stream flowing in line 3. In second mixing zone 6, the effluent from rst mixing zone 2 is mixed with fresh concentrated sulfuric acid, preferably oleum, in strength and amounts sufficient to secure the desired depth of sulfonation. i It has been found that with vigorous mixing in second mixing zone 6 a substantial portion of the total sulfonationY desired is completed at or n ear the point of mixing; the reaction is very rapid, with experiments indicating that as much as 50% of the total reaction is completed within the first second with each increment of fresh acid added to mixing zone 6. Thus, it may be seen that in the present process it is possible to accomplish substantial sulfonation out of contact with the unsulfonated oil in reactor-settler 9 and thereby to greatly increase meta-xylene sulfonation selectivity and acid utilization etiiciency. The effluent from second mixing Zone 6 is passed through line 8 to reactor-settler 9 and is passed upwardly therethrough at relatively low velocity, for example 2 to 8 ft./min., and preferably about 5 ft./min. The unsulfonated oil coalesces and flows upwardly in reactor-settler 9 at a greater rate than the acid sludge phase because of its lower density. Reactor-settler 9 serves a three-fold purpose: (l) it provides residence time for a continuation of the sulfonation reaction; (2) it provides settling time for the net unsulfonatedoil that separates from the acid phase; and (3) it provides settling volume for the net acid phase sludge produced. Residence time -in reactor-settler 9 for the eluent from second mixing zone 6 may be from about l to 3 hours, and preferably about 2 hours. Some sulfonation of xylenes continues in reactor-settler 9; however, the major portion of the desired sulfonation has been accomplished bythe time the effluent from second mixing zone 6 reach reactor-settler 9. Because of coalescence and its low density the unsulfonated oil phase rises to form layer l16 in reactor-settler 9 above the acid ,phase 17 therein.

From reactor-settler 9 the recycle acid stream hereinbefore described is withdrawn through line 3 from a pocket formed in acid phase 17 by barrier 15, provided to prevent unnecessary turbulence. From reactor-settler 9 an acid sludge-free stream of unsulfonated oil is Withdrawn through line 18 and passed to distillation system 5S -for removal of small amounts of polymers and color bodies through line 57. Recovered unsulfonated oil is withdrawn through line 56.

From reactor-settler 9 a portion of acid phase 17 is continuously withdrawn as a stream by way of a pocket formed by barrier and is passed through line 19 into contact with a stream of water ilowing in line 20. This `withdrawn stream may contain, as meta-Xyleue sulfonic acid, about 50% `of the meta-xylene that entered the system in the feed in line 1. Further, the meta-xylene sulfonic acid present in the stream may ybe about 85% of the total sulfonic acids present in the stream. The stream also contains a quantity of dissolved unsulfonated oil that must be removed to prevent its adverse effect on the purity of lthe meta-Xylene subsequently separated from the meta-xylene sulfonic acid. This uusulfonated oil is removed from the stream by steam stripping in convenlOnal Steam stripper 25, after a sufficient amount of water has been added through line 20 to reduce the concentration of the sulfuric acid in line 19 to about 70%. The thus diluted stream which enters steam stripper through line 19 is passed downwardly through steam stripper 25 in countercurrent contact with steam introduced into steam stripper 25 through line 26. Steam stripper 25, which may be a conventional packed countercurrent bons and steam are withdrawn Afrom steam stripper 25 through line 27 and are condensed in condenser 28. The hydrocarbons so condensed are then passed from condenser 28 through line 29 to line 18 for further processing as hereinbefore described. 'Ihe stripped sludge stream from steam stripper 25 is passed through line 37 to rst hydrolyzer 39, after having been heated in heat exchanger 40 and diluted with water introduced through line 38 to an extent sufficient to obtain a desired amount of hydrolysis in rst hydrolyzer 39 within a desired time. For example, the stream in line 37 may be heated to about 310 F. by heat exchanger 40 and suicient water may be introduced through line 3S to reduce the sulfuric acid concentration in the stream in line 37 to about 28%. Under these conditions sutiicient hydrolysis to obtain aproduction of pure meta-xylene may be obtained with a residence time in first hydrolyzer 39 of about 1.5 hours. The acid layer from iirst hydrolyzer 39 is passed through line 47 and heat exchanger 43 to second hydrolyzer 48. In heat exchanger 43 this acid layer is heated to, Afor example, 375 F., to facilitate hydrolysis in second hydrolyzer 48. A residence time of about two hours in second hydrolyzer 48 suflices to hydrolyze the remaining sulfonic acids in this acid layer. A hydrocarbon stream lean in meta-xylene is passed from second hydrolyzer 48 through line '.50 to line 1g for subsequent processing as hereinbefore described. From second hydrolyzer 48 sulfuric acid of, for example, 55% concentration is recovered through line 49.

A hydrolysis product from iirst hydrolyzer 39 is passed through line 41 to convention distillation system 42. In distillation system 42 a small quantity of polymers and color bodies are separated and withdrawn through line 45, and a net product stream of meta-xylene of at least 95% purity is withdrawn through line 46.

The foregoing detailed description of the operation of the illustrated embodiment of the present invention will be better understood from the following example, which is illustrative of process conditions during a typical operation of the embodiment shown.

t EXAMPLE 3 Feed in line 1 7 The sltocllr indicated in Ex- Recycle acid sludge in line 3-- Flow rute about 19 vols. re-

cycle sludge/vol. fecd in line 1; 150 F. 81% HaSOl concentration.

Line 4 temperatureV downstream from heat exchanger 20% filming H2SO4 (110W rate chosen to result in desired depth of sulfonation).

Average temperature of con- Acid in line 7 V Reactor-settler 9 tents F. residence time for contents two hours.

` 1% dissolved oil Steam stripper 25 Packed, countercurrent stripper.

Line 47, downstream from heat exchanger 43 375 F.

Second hydrolyzer 48 2.0 hours residence time for contents; substantially complete hydrolysis of sulfonic acids in contents.

Line 49 55% H2SO4, recovered for subsequent refortiiication; ow rate about 0.38 vol./ vol. feed in linel.

Line 46 95% purity meta-Xylene: flow rate about 0.19 vol./ vol. feed in linel.

Line 56 Hydrocarbons containing 34 vol. percent meta-xylene, 22 vol. percent para-xylene, 9 vol. percent ortho-xylene, 19 vol. percent ethyl benzene, and 16 vol. percent non-aromatics; flow rate about 0.77 vol./vol. feed in line 1.

It will be seen from the foregoing that, in contrast to previous processes, a major portion of the sulfonation in the process of'lthe present invention is accomplished out of the presence of the relatively large amounts of the relatively low meta-xylene content unsulfonated oil n large quantities of undesired isomers of meta-xylene present in'layer 16. These improved results are `further illustrated by the lfollowing Examples 4 and 5, in each of which the runs were continuously made in laboratory scale equipmentY comprising a reactor-settler 9, first mixing zone Q., .and second mixing zone 6, arranged and connected as shown in the drawing. In Example 4 the contents of reactor-settler 9 were stirred, so that the recycle stream in line 3 would contain a mixture of the sulfonic acids and accumulated -unsulfonated oil from reactorsettler 9, and therefore so that sulfonation in second mixing zone 6 would be accomplished Iin the presence of accumulated unsulfonated oil, to simulate practice in .previous processes. In Example reactor-settler 9 was not stirred, so that the recycle stream in line 3 would be substantially free of unsulfonated oil, in accordance with the present invention. In all runs in both Examples 4 and 5 the line 1 feed composition was 45.7 vol percent meta-xylene, 37.1 vol. percent other Cs isomers, and 17.2 vol. percent paratlins, and .the acid used was 20% fuming HZSO.,l (expressed in Examples 4 and 5 in terms of equivaient 100% H2804).

`rIf depth of sulfonation isl plotted against selectivity;

for each of Examples 4 and 5, the following selectivities" for even intervals of sulfonation depth may be obtained from the resulting curves:

Example 6 Example 7 (from data (from data Depth of Sultonatlon, wt. percent. of Ex. 4) of Ex. 5)

10 Y Se1eetlvity, wt. percent an 86.0 sa o 35 84. 9 87. 7V

In both Examples 6 and 7 it is seen th'at selectivity decreases as depth of sulfonation increases, but it may alsol be seen that the method of the present invention (Example 7) results in higher selectivity for a given sultonation depth, throughout the range of the data, than the method (Example 6) wherein sulfonation was carried out in the presence of accumulated unsulfonated loil to simulatepractice in previous processes.

In the practice of the present invention it is desirable that the recycle acid sludge stream in line 3 iiow at the rate of at least l0 volumes of acid sludge per volume of feed in line 1, and preferably 'between 15 and 20'volurnes 0f recycle per volume vof feed, because thereby substantially optimumk meta-xylene sulfonation selectivitypmay be obtained. This is illustrated by the following Example 8, which shows data derived from aseriesofcontinuous runs made with identical feed and with the equipment arrangement used to obtain the data in Examples?. and 5;

the observed selectivities were adjusted to` a common depth of sulfonation to give the selectivities shown.

. From Example 8 it will be seen that little gain results from increasing above about 20:1V the ratio of the ow rate in line 3 to the iiow rate inV line 1, and in view EXAMPLE 4 selectivity, in Depth 0i sulterms of the Ratio oi Mol ratio t ionation, in meta-xylene line 3 of line 7 Line 3 terms of total sulfonic acid Run No. recycke acid to recycle Cs aromatics content of rate to 1 line 1 temperainline 1 that the total feed rate metaf ture, F. are sulfonated, Og aromatic xylene wt. percent sulfonic acids in line 19, wt. percent EXAMPLE 5 1 of recycle pumping costs, :1 is therefore a practical upper limit, despite, the. fact. thatv the data'V do show a metafxylene; sulfonatiom selectivityf increase atleast up to a 200:1 recycle ratio.

By the terms first mixing zone 2 and second mixing zone' 6; as' used hereinv is meant any means capable of eecting' al highe degree of turbulence such as may be obtainedw with linebafes, orifice plates andlventuri. sections. Those skilled in the art will appreciate that such means may. comprise pumps, baflle sections in heat exchangers, andthe. like. which,.if capable of accomplishing. the desired highturbulence mixing, may dispense withY the necessity for process equipment designed pri:- marily for mixing. The pipe diameters for lines between. mixing zones 2 and 6,A and between mixing, zone 6 and reactor-settler 9, preferably should be selected to provide flow velocities characterized by. a Reynolds. number well within the turbulent region. Vigorous mixing is. especially desirable in second mixing zone 6.A Such mixing, coupled with the addition of the recycle, sulfonic acids and free acid in the previous mixing zone 2,. minimizes those local and momentary high acid concentrations, in mixing zone 6, which otherwise would adversely affect meta-xylene sulfonation selectivity.-

From the foregoing itmay be seen that withv the, process of the present invention meta-xylene of high puritymay be produced from hydrocarbon mixtures comprising meta-xylene and at .least one other xylene isomer` with high metaxylene sulfonation selectivityV and. eicient. acid utilization.

Although only specific arrangements and modes of construction and operation of the present invention have been described and illustrated, numerous changes could be made in those arrangements and modes without departing from the spirit of the invention, and. all such changes that fall Within the scope of the appended claims are intended to be embraced thereby.

What is claimed is:

l. A continuous process for separating metaxylene. from hydrocarbon feeds consisting predominantly of xylene isomers and having a` substantial content' of rnetaxylene which comprises passing one volume of the hydrocarbon feed with at: least 10 volumes of a recycle stream consisting essentially ofrxylene sulfonic acids and sulfuric acid into a first mixing zone, the xylene sulfonic acid component of the recycle stream consisting predomi# nantly of metaxylene sulfonic acid and the sulfuric acid component of the recycle stream having a concentration below that necessary for effective sulfonationat the ternperature of saidfirstmixing-zone, passing-- the effluent from the first mixing zone into a second mixing zone together with concentrated sulfuric acid, the quantity of concentrated sulfuric acidi introduced into the second mixing zone being suicient to sulfonate not more. than about of the aromatic hydrocarbons contained in the feed at the temperature prevailing in the second mixing zone and in the reactor-settler zone referred to hereinafter, passing the etuent from the second mixingzone into a reactor-settler zone to separate a hydrocarbon phase and a xylene sulfonic acid-sulfuric acid phase, Withdrawing the hydrocarbon phase from the reactor-settler zone, withdrawing the major portion of the xylene sulfonic acid-sulfuric acid phase to constitute the recycle stream, and withdrawing the minor proportion of said phase and subjecting it to hydrolysis under hydrolysis4 conditions to liberate a metaxylene rich product.

2. A process for separating meta-xylene of hi'ghpurity from a first mixture comprising meta-xylene and at least one other xylene isomer, which comprises: contacting said tirst mixture in a rst contacting zone with a recycle stream comprising xylene sulfonic acids and sulfuric acid having a concentration below that necessary for sulfona# tion of xylenes at the temperature of said rst contacting zone; passing the resulting second mixture to a; second contacting zone and there contacting said second mixture with concentrated fresh sulfuric acid; separating from the resulting third mixture a first phase substantiallyA com.- prisingunsulfonatedA oil lean in meta-xylene and a second phase comprising xylene sulfonic acids but substantially free fromt unsulfonated oil; obtaining said recycle stream from a portion of said separated second phase; and recovering meta-xylene' from the remaining, portion. of saidn separated second phase.

. 3i. A process for separating high-purity meta-xylene' from: a iirst` hydrocarbon! mixture of xylene isomers including meta-xylene, whichcomprises: forming a second` mixture comprising said first mixture, sulfonic acids and sulfuric acidhavinga concentration insuicient to cause substantiah sulfonat-ion at the temperature of said second' ixture; selectively sulfonating meta-xylene in said second mixturewit-lr. concentrated fresh sulfuric acid, to produce a third; mixtureV comprising sulfonic acids and unsulfonated hydrocarbons; substantially separating said sulfonic acids from said unsulfonated hydrocarbons; utilizing a portion of. said separated sulfonic acids to form said second mixture; and recovering meta-xylene from the remaining portion of said separated sulfonic acids.

4; A process as in claim 3,. in which meta-xylene is recovered from said remaining portion of saidseparated sulfonic acids by: contacting saidy remaining portionwith water to reduce the concentration of the sulfuric acid. therein; steam stripping the resulting' stream comprising said remaining portion and water to.- remove: dissolved unsulfonated oil therefrom; contacting the stripped stream with water to reduce4 the: concentration. of the sulfuric acid therein; hydrolyzing` in a. rst: hydrolysis stage at. a` temperature above` the atmospheric boiling temperature of metaxylene a substantial portion. of. the: sulfonic acids: in the resulting stream comprising said stripped stream and water; separating the products: of

said rst` hydrolysis stagev into` an acid. layer fraction and a hydrocarbon fraction richl in meta xylene; separating high-purity meta-xylene from said hydrocarbon fraction by distillation; hydrolyzing in a second hydrolysis` stage` sulfonic acidsA in said acid layer fraction; and separating the products of said second hydrolysis stage. into. an acid layer fraction and' a hydrocarbon -fractionf lean in meta.- xylene.

5. A process as in claim 4, in which said unsulfonated hydrocarbons separated from said' third; mixture, said: dissolvedV unsulfonatedoil removed byf said steaml stripping, and said hydrocarbon.` fraction from said second hydrolysis stage are passed] toa distillation system for recovering therefrom a hydrocarbon product lean in meta-xylene.

6. In a proces for separating meta-xylene frorntaxhydrocarbon feed comprising meta-xylene andl at leastioneiother xylene isomer by differentialA sulfonation in a sulfonation zone to produce a mixture comprising xylene sulfonic acids, and by subsequent separation of meta-xylene from said mixture, theimprovement which comprises: continuously supplying said. feed to said. zone. in admixture. with a recycle stream containing xylene sulfonic acids rich in metaxylene sulfonic acid and containing sulfuric acid at a concentration insucient to cause sulfonation at the temperature of said zone, continuously supplying concentrated sulfuric acid to: said zone, maintaining the contents of said zone in a highly turbulent state under conditions effective to produce a desired depth of sulfonation, continuously withdrawing from said zone a reaction mixture comprising xylene sulfonic acids sulfuric acid and unsulfonated oil, separating from saidl reaction mixture a phase comprising said xylene sulfonic acids andl sulfuric acid but substantalliI free from said unsulfonated oil, recovering meta-xylene from a portion of said phase, and continuously recycling another portion of said phase into admxture with said hydrocarbon feed to said zone.

(References onfollowing page) 9 References Cited in the le of this patent OTHER REFERENCES UNITED STATES PATENTS Brooks et al.: The Chemistry of Petroleum Hydrocar 2,470,896 Mavity May 24, 1949 bons, v01. III, Reinhold Publishing Corp. 430 Park 25 11,711 Hetzner June 13 1950 5 Avenue, New York 22, N.Y., page 615.

2,519,336 Beach et a1. Aug. 22, 1950 2,848,483 Reif et a1. Aug. 19, 1959 

1. A CONTINUOUS PROCESS FOR SEPARATING METAXYLENE FROM HYDROCARBON FEEDS CONSISTING PREDOMINANTLY OF XYLENE ISOMERS AND HAVING A SUBSTANTIAL CONTENT OF METAXYLENE WHICH COMPRISES PASSING ONE VOLUME OF THE HYDROCARBON FEED WITH AT LEAST 10 VOLUMES OF A RECYCLE STREAM CONSISTING ESSENTIALLY OF XYLENE SULFONIC ACIDS AND SULFURIC ACID INTO A FIRST MIXING ZONE, THE XYLENE SULFONIC ACID COMPONENT OF THE RECYCLE STREAM CONSISTING PREDOMINANTLY OF METAXYLENE SULFONIC ACID AND THE SULFURIC ACID COMPONENT OF THE RECYCLE STREAM HAVING A CONCENTRATION BELOW THAT NECESSARY FOR EFFECTIVE SULFONATION AT THE TEMPERATURE OF SAID FIRST MIXING ZONE, PASSING THE EFFLUENT FROM THE FIRST MIXING ZONE INTO A SECOND MIXING ZONE TOGETHER WITH CONCENTRATED SULFURIC ACID, THE QUANTITY OF CONCENTRATED SULFURIC ACID INTRODUCED INTO THE SECOND MIXING ZONE BEING SUFFICIENT TO SULFONATE NOT MORE THAN ABOUT 50% OF THE AROMATIC HYDROCARBONS CONTAINED IN THE FEED AT THE TEMPERATURE PREVAILING IN THE SECOND MIXING ZONE AND IN THE REACTOR-SETTLER ZONE REFERRED TO HEREINAFTER, PASSING THE EFFLUENT FROM THE SECOND MIXING ZONE INTO A REACTOR-SETTLER ZONE TO SEPARATE A HYDROCARBON PHASE AND A XYLENE SULFONIC ACID-SULFURIC ACID PHASE, WITHDRAWING THE HYDROCARBON PHASE FROM THE REACTOR-SETTLER ZONE, WITHDRAWING THE MAJOR PORTION OF THE XYLENE SULFONIC ACID-SULFURIC ACID PHASE TO CONSTITUTE THE RECYCLE STREAM, AND WITHDRAWING THE MINOR PROPORTION OF SAID PHASE AND SUBJECTING IT TO HYDROLYSIS UNDER HYDROLYSIS CONDITIONS TO LIBERATE A METAXYLENE RICH PRODUCT. 